During recent years, there has been an increase in the use of antennas that include an array of antenna elements, one example of which is a phased array antenna. Antennas of this type have many applications in commercial and defense markets, such as communication and radar systems. In many of these applications, broadband performance is desirable. In this regard, some of these antennas are designed so that they can be switched between two or more discrete frequency bands. Thus, at any given time, the antenna is operating in only one of these multiple bands. However, in order to achieve true broadband operation, an antenna needs to be capable of satisfactory operation in a single wide frequency band, without the need to switch between two or more discrete frequency bands.
One type of antenna element that has been found to work well in an array antenna is commonly referred to as a tapered slot antenna element. The spacing between antenna elements in an array antenna is inversely proportional to the frequency at which the antenna operates, and a tapered slot antenna element fits comfortably within the space available for antenna elements in many array antennas, including those which operate at high frequencies.
Tapered slot antenna elements typically have a bandwidth of about 3:1 or 4:1, although some very recent designs have achieved a maximum bandwidth of about 10:1, or in other words one decade. While these existing tapered slot antenna elements have been generally adequate for their intended purposes, they have not been satisfactory in all respects. In this regard, there are applications in which it is desirable for a tapered slot antenna element to provide good performance across a bandwidth in the range of approximately two to four decades, or even more. Existing designs and design techniques have not been able to provide a tapered slot antenna element which approaches this desired level of broadband performance.